1. Field of the Invention
The present invention relates generally to image projection apparatuses.
2. Description of the Related Art
In recent years, DLP (Digital Light Processing) projectors that use DMDs (Digital Micro-mirror Devices) and LCD (Liquid Crystal Display) projectors that use transmissive liquid crystal are widespread as image projection apparatuses capable of displaying an image in an enlarged manner by projecting the image onto a projection receiving part, such as a screen; this is because these projectors are relatively inexpensive, light-weight, and compact.
Such a projector typically uses a discharge lamp, e.g., a high-pressure mercury lamp, or a semiconductor light source (solid-state light source), e.g., an LED (Light-Emitting Diode) or an LD (Laser Diode), as a light source. To suppress temperature rise of optical components, such as an internal lens, mirror, DMD, and liquid crystal, caused by heat and the like liberated from the light source, techniques of cooling inside the projector using a cooling fan or the like have been developed. An example of such a technique is disclosed in Japanese Patent No. 3471772.
Japanese Patent No. 3471772 discloses a projector-related method of detecting a rise in temperature of an optical component or ambient air temperature and, increasing the voltage applied to a cooling fan to increase rotational speed of the cooling fan when it is determined that a voltage applied to the fan can be increased but changing electric power supplied to a light source when it is determined that the applied voltage is at its upper limit, to maintaining a temperature of each part within the rating.
However, the technique disclosed in Japanese Patent No. 3471772 is disadvantageous in that changing the electric power supplied to the light source can undesirably lower brightness of an image projected by the projector. Hence, there is a need for developing a technique that enables efficient cooling while maintaining image brightness.